Positioning of posts in liquid crystal valves for a projection display device

ABSTRACT

A liquid crystal display device having pillar-shaped spacers formed in pixel array regions is provided with improved display quality by preventing the degradation of contrast and the occurrence of residual images. A plurality of pillar-shape spacers formed in their pixel array regions are provided at locations which do not overlap with each other when images are projected on the screen using three different liquid crystal light valves to project the red (R), green (G) and blue (B), constituents of images.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a liquid crystal display device and amethod for the manufacture thereof, and more specifically, to aprojection-type liquid crystal display device using liquid crystal lightvalves, and a method for the manufacture thereof.

2. Description of the Prior Art

In recent years, a projection type liquid crystal display device hasassumed a new prominence as a potential ultra-high definition displaydevice which replaces CRTs. The projection type liquid crystal displaydevice has already been used in HDTV or OEP displays.

The projection optical system of the projection type liquid crystaldisplay device consists of a light source, light valves, a screen,optical filters, and projection lenses. Liquid crystal panels are usedas the light valves. Light valves are classified into a transmissiontype liquid crystal light valve, which transmits light from the lightsource and projects images on the screen, and a reflection type liquidcrystal light valve, which reflects light from the light source andprojects images on the screen. Since liquid crystal light valvesgenerally reflect/transmit the lights of three primary colors, red (R).green (G). and blue (B), three light valves are used in a projectiontype liquid crystal display device.

A liquid crystal display device of the active matrix type consistsgenerally of an array substrate on which there are interconnectedswitching elements and display electrodes and a counter substrate onwhich there are a counter electrode facing to the array substrate at apredetermined distance (cell gap) from the array substrate. Liquidcrystal material is enclosed between the array substrate and the countersubstrate.

In order to achieve desired electro-optical properties of the liquidcrystal, the predetermined cell gap must be maintained evenly throughoutthe entire display surface of the panel. To accomplish this, somedisplay devices use a large number of glass or plastic beads having adiameter of several microns dispersed on the panel as spacers to makethe cell gap even. However, this method with using spacers has problemsof the uniformity of beads diameters and difficulty in the evendispersion of spacer beads on the panel, as well as the loss of lightdue to spacers on pixels.

Instead of the above spacer bead dispersion method, a method has beenproposed of forming columns consisting of an insulation film and thelike in the cell gap as spacers. In this method, columns of a siliconoxide film are formed in the cell gap as spacers (pillar-shape spacers).by using photolithography commonly used in the manufacturing process ofsemiconductor devices. This method is advantageous compared with theconventional method of using spacer beads in that a cell gap is formedwith a high accuracy.

For example, in some reflection type liquid crystal light valves where asilicon substrate is used as the array substrate, an MOS transistor asthe switching element and an aluminum (Al) reflecting film connected tosaid MOS transistor are provided on the array substrate for eachelement, and a plurality of pillar-shape spacers are formed in theshaded on black matrix region between reflecting films.

In a projection type liquid crystal display device which displayshigh-definition images on a large screen, the improvement of displaybrightness is important.

In order to improve display brightness an increase in the numericalaperture of subpixels is considered. In a reflection type liquid crystallight valve, pillar-shape spacers are formed between two reflectingfilms, and the ends of the spacers override the reflecting films todecrease the reflection area of the reflecting films, causing thenumerical aperture of subpixels to lower.

Also in the cell gap forming system using such pillar-shape spacers,even if the overriding of spacers on the reflecting films as describedabove could be prevented not to affect the numerical aperture, otherfactors lowering display qualities still remain.

First, where there are pillar-shape spacers formed between reflectingfilms, the application of an oriented film is affected by projectingpillar-shape spacers. The uneven application of the oriented film makesit difficult to obtain a cell gap which is even throughout the surface,and may cause the cell gap to vary. The regions of varied cell gap donot provide same contrast obtained from the proper cell gap.

Second, reverse tilt occurs in liquid crystals present in the closevicinity of the of the spacers cause reverse tilt due to thepillar-shape spacers. As a result of this disturbance of orientation adiscontinuity is observed as a line, known as a disclination line,occurs causing contrast to lower, and residual images to occur.

In a projection type liquid crystal display device, where three lightvalves are used for three primary colors, red (R), green (G) and blue(B) to display enlarged images on a large screen, decreases in numericalaperture, and contrast due to the variation of the cell gap, and theoccurrence of disclination lines are particularly noticable.

The disturbance of liquid crystal orientation of pixels cannot beavoided as long as pillar-shape spacers are present on the pixel regioncontributing to the display. In high-definition, large-screenprojectors, the disturbance of liquid crystal orientation is enlarged,and projected on the screen as the screen becomes larger, causing theincreased degradation of the display quality.

It is an object of the present invention to provide improved displayquality in a liquid crystal display device comprising pillar-shapespacers formed in the pixel array region by preventing contrast fromdegrading and residual images from occurring. Another object of theinvention is to provide a method for the manufacture of such a liquidcrystal display device.

SUMMARY OF THE INVENTION

The above object is achieved by a liquid crystal display devicecomprising three liquid crystal light valves for displaying imagescorresponding to red (R), green (G) and blue (B) each having a pluralityof pillar-shape spacers formed in the pixel array region for maintaininga prescribed cell gap, wherein, said pillar-shape spacers formed in thepixel array region in each of said three liquid crystal light valves areprovided at locations where at least a part of the pillar-shape spacersdo not overlap with each other when images ere projected on the screen.

Also, the above object is achieved by a liquid crystal display device,wherein, said pillar-shape spacers formed in the pixel array region ineach of said three liquid crystal light valves are provided at locationsregularly shifted from each other when images are projected on thescreen.

Furthermore, the above object is achieved by a liquid crystal displaydevice, wherein said pillar-shape spacers formed in the pixel arrayregion in each of said three liquid crystal light valves are provided atlocations shifted from each other by an equal distance when images areprojected on the screen.

Furthermore, the above object is achieved by using a method for themanufacture of a liquid crystal display device comprising steps of,patterning resist layers over said pixel array region by shiftingrelative to each other substrate side alignment marks, provided on thesubstrate on which the pixel array region are formed, and mask sidealignment marks, provided on the mask for pillar-shape spacerscorresponding to said substrate side alignment, for each of pixel arrayregions for red (R), green (G) and blue (B); etching the underlyinginsulation film using said patterned resist layer as the mask; andforming a plurality of pillar-shape spacers shifted from each other ineach of said pixel array regions for red (R), green (G) and blue (B).

According to the present invention, the influence of pillar-shapespacers on display qualities is dispersed by preventing the locations ofa plurality of pillar-shape spacers, formed in each pixel array regionof three liquid crystal light valves, from overlapping on the screen. Asa result the disturbance of liquid crystal orientation is minimized whenimages are enlarged and projected by the three liquid crystal lightvalves.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partly sectional view showing two adjacent two pixels of areflection type liquid crystal light valve used in an embodiment of thepresent invention;

FIG. 2 is a partial top view showing a reflection type liquid crystallight valve for red;

FIG. 3 is a partial top view showing a reflection type liquid crystallight valve for green;

FIG. 4 is a partial top view showing a reflection type liquid crystallight valve for blue;

FIG. 5 is a schematic diagram showing a reflection type liquid crystaldisplay device using reflection type liquid crystal light valvesaccording to the embodiment of the present invention;

FIG. 6 is a perspective projection of piled pixel array regions 4 ofthree light valves shown in FIGS. 2-4;

FIG. 7 is a top view showing a part of the pixel array regions 4 formedon the surface of the silicon substrates 2;

FIG. 8 is a diagram showing the patterning mask 32 of pillar-shapespacers used in the embodiment of the present invention;

FIG. 9 is a diagram showing patterning of pillar-shape spacers of theliquid crystal light valve for red;

FIG. 10 is a diagram showing patterning of pillar-shape spacers of theliquid crystal light valve for green; and

FIG. 11 is a diagram showing patterning of pillar-shape spacers of theliquid crystal light valve for blue.

DETAILED DESCRIPTION OF THE INVENTION

A liquid crystal display device and a method for the manufacture thereofaccording to an embodiment of the present invention will be describedreferring to FIGS. 1 to 11.

FIG. 1 is a partly sectional view showing two adjacent pixels of areflection type liquid crystal light valve used in this embodiment.

A transistor 104, of which detailed diagram is omitted, is formed on asilicon substrate 100. Over the silicon substrate 100 and the transistor104, a silicon oxide film 102 having a thickness of about 2 μm isformed, and over the silicon oxide film 102, a light absorbing layer 106is formed. Over the light absorbing layer 106, a silicon nitride film108 having a thickness of 5,000 Åis formed, over which a lightreflecting film 112 consisting of Al having a thickness of 1,500 Å isformed.

The light reflecting film 112 is connected to the source electrode (notshown) of the transistor 104 by a tungsten (W) stud. 110 buried in thethrough hole formed through the silicon oxide film 102 and the siliconnitride film 108, and also acts as the display electrode for drivingliquid crystals. One light reflecting film 112 constitutes the subpixelof one display pixel.

No Al layers are formed between light reflecting films 112 adjacent toeach other (distance: about 1.7 μm), and as FIG. 1 shows, thepillar-shape spacers 118 of a silicon oxide film of a height of about 5μm are formed between specified light reflecting films 112.

In the sectional diagram of FIG. 1, about 1 μm of the pillar-shapespacer 118 overrides the light reflecting film 112 at both edges. Aglass protection substrate 116, which is the counter substrate, isformed on the other end of the spacer 118. A counter electrode 114 isformed over the entire surface of the light reflecting film side of theglass protection substrate 116. Light crystals are enclosed in the cellgap of a thickness of about 5 μm produced by the spacer 118, forming aliquid crystal layer 120.

The transistor 104 is an FET (field-effect transistor) comprising asource electrode, a drain electrode connected to a data line, and a gateelectrode connected to a scanning line (not shown), and act as aswitching element which supplies voltage, impressed on the data linewhen the gate is in ON-state, to the light reflecting film 112, which isthe display electrode.

Changing the light transmittivity is accomplished by changing theorientation of liquid crystal molecules 122 using voltage impressedbetween the light reflecting film 112, which is the display electrode,and the counter electrode 114. When the transistor 104 is ON, lightincident from the glass protection substrate 116 side is eithertransmitted to the light reflecting film 112, reflected, and allowed tooutgo through the glass protection substrate 116, or not transmitted.

FIGS. 2-4 are partial top Views showing reflection type liquid crystallight valves. FIG. 2 shows a reflection type liquid crystal light valvefor red; FIG. 3 shows a reflection type liquid crystal light valve forgreen; and FIG. 4 shows a reflection type liquid crystal light valve forblue.

In these figures, the same part of the pixel array region of reflectiontype liquid crystal light valves is illustrated. A pixel array region 4is formed on the array side substrate 2 of the reflection type liquidcrystal light valve. The pixel array region 4 has pixels as shown inFIG. 1 arranged vertically and horizontally as, for example, in a2,000×2,000 matrix.

Between adjacent pixels 6, there is a black matrix material 8 forming alight shield region. As shown in FIG. 2, part of each of thepillar-shaped spacers 10 of the reflection type liquid crystal lightvalve overlies four adjacent pixels 6 and the black matrix material 8 atthe intersection of those four pixels.

Therefore the light reflecting area of the light reflecting film in thefour pixels 6 on which a part of the pillar-shaped spacers 10 overliesis decreased, and the size of the pixel aperture is reduced.

Also, there may be unevenness on the orientation film of the four pixels6. Furthermore, disclination lines may occur due to the disturbance oforientation of this region.

The pillar-shaped spacers 10 are positioned each nine pixels in both therow and column directions of the matrix.

Therefore, about 50,000 pillar-shape spacers 10 are formed in the entirepixel array region 4.

In FIGS. 3 and 4, as shown in FIG. 2, pillar-shape spacers 12 and 14 areformed in pixel array regions of reflection type liquid crystal lightvalves for green and blue, respectively. However, the pillar-shapespacers 12 of the light valve for green are arranged, for example, atthree pixel spaces from pillar-shape spacers 10 of the light valve forred shown in the lower left of FIG. 2 in both row (+X) and column (+Y)directions.

Similarly, the pillar-shape spacers 14 of the light valve for blue arearranged at six pixel spaces from pillar-shape spacers 10 of the lightvalve for red in both row (+X) and column (+Y) directions, therefore atthree pixel spaces from pillar-shape spacers 12 of the light valve forgreen in both row (+X) and column (+Y) directions.

A projection type liquid crystal display device in which thesereflection type liquid crystal light valves for red, green and blue arecombined will be described referring to FIG. 5. FIG. 5 is a schematicdiagram of a projection type liquid crystal display device usingreflection type liquid crystal light valves according to thisembodiment.

Light linearly polarized ongoing from the light source 42 is reflectedby a polarizing beam splitter 44, and enters in a color separation prism46, where it is separated into three primary colors of red (R), green(G) and blue (B), which are incident to reflection type light valves forred (R), green (G) and blue (B) 48, 50 and 52, respectively.

The light, brightness modulated for each subpixel by each reflectiontype liquid crystal light valve is reflected and again enters in thecolor separation prism 46, where it becomes linearly polarized lightdeviated by 90 degrees from the original polarized light, and isincident to the polarized beam splitter 44. The reflected lights formreflection type liquid crystal light valves 48, 50 and 52 are incidentto the projection lens 54 through the polarized beam splitter 44,enlarged, and projected on to the screen 56.

FIG. 6 is a perspective projection of piled pixel array regions 4 ofthree light valves shown in FIGS. 2-4. By placing pillar-shape spacers10, 12 and 14 as described above, all the spacers are arranged withregular deviation without overlapping. That is, when images areprojected using the projection type liquid crystal display device, theimages are projected on to the screen 56 in the state shown in FIG. 6.

Be arranging the pillar-shape spacers of liquid crystal light valves forthe three colors, the influence of pillar-shape spacers, such as adecrease in numerical aperture, uneven orientation films, and theoccurrence of disclination due to the disturbance of orientation, isdispersed, and the problems such as the reduction of contrast onprojecting or residual images are practically eliminated.

Next, a method for the manufacture of the reflection type liquid crystallight valves used in this embodiment will be described referring toFIGS. 7 to 11.

The unique feature in the method for the manufacture of the reflectiontype liquid crystal light valves according to this embodiment is themethod for forming pillar-shape spacers, is described. Howeverconventional manufacturing steps such as the formation of elements inthe array substrate side, bonding the array substrate after pillar-shapespacers have been formed to the counter substrate, and the injection ofliquid crystals, are omitted.

FIG. 7 is a top view showing a part of the pixel array region 4 formedon the surface of a silicon substrate 2. Almost square light reflectingfilms 6 are formed in the pixel array region 4 as a matrix, and blackmatrices 8 having a light shielding function are formed between lightreflecting films 6. A scribe line (not shown), used in cutting thesubstrate in the subsequent process, is formed in the Y-axis directionto the left of the pixel array region 4, and the alignment marks 22 inthe array substrate side used in the formation of pillar-shape spacersare patterned in the prescribed locations in the scribe line.

The alignment marks 22 in the array substrate side comprise alignmentsubmarks 16, 18 and 20 used for forming prescribed pillar-shape spacersin reflection type liquid crystal light valves for red (R), green (G)and blue (B). These submarks are arranged, in this embodiment, in the Ydirection in the order of blue, green and red from the bottom with adistance of 13 pixels between them.

FIG. 8 shows the patterning mask 32 of pillar-shape spacers used in thisembodiment. The spacer mask 32 consists, for example, of a transparentglass substrate, on which circular patterns 34 are formed, for example,of chromium for patterning pillar-shape spacers in a matrix. The pattern34 is repeated every nine pixels in this embodiment.

The alignment marks 30 of the mask side used in the patterning ofpillar-shape spacers are formed to the left of the pattern 34corresponding to alignment marks 22 of the array substrate side shown inFIG. 7.

The alignment marks 30 of the mask side comprise alignment submarks 24,26 and 28 used for forming prescribed pillar-shape spacers in reflectiontype liquid crystal light valves for red (R), green (G) and blue (B).These submarks are arranged, for example in this embodiment, in theorder of blue, green and red from the bottom left with a distancesbetween them of 3 pixels in X direction and 10 pixels in Y direction.

A silicon oxide film of a thickness, for example, of 5 μm for formingpillar-shape spacers are deposited of the entire surface of the siliconsubstrate 2 shown in FIG. 7 by the plasma CVD method. Next, a positivephotoresist is applied in a thickness, for example, of 4 μm on theentire surface to form a photoresist layer.

The silicon substrate 2, on which the silicon oxide film and thephotoresist layer are formed is placed on the X-Y stage of, for example,exposure equipment such as a mask aligner (not shown), and the mask 32shown in FIG. 8 is set between the stage and the light source of theexposure equipment.

FIG. 9 is a diagram showing the patterning of the pillar-shape spacersof the liquid crystal light valve for red.

The X-Y stage of the exposure equipment is moved to align the alignmentsubmark for red 16 of the substrate side alignment marks 22 with thealignment submark for red 24 of the mask side alignment marks 30, andexposure is performed.

After exposure, patterning is performed to form the resist layer as theetching mask on the pillar-shape spacer forming location. Thereafter,the silicon oxide film is etched using this resist layer as the mask tocomplete the desired pillar-shape spacer 10.

When the exposure of the substrate for forming the light valve for redhas been completed, the substrate is removed from the exposureequipment, another silicon substrate 2 on which a silicon oxide film andthe photoresist layer have been formed is loaded on the X-Y stage of theexposure equipment, and the exposure of the substrate for forming thelight valve for green is performed.

The X-Y stage of the exposure equipment is moved to align the alignmentsubmark for green 18 of the substrate side alignment marks 22 with thealignment submark for green 26 of the mask side alignment marks 30, andexposure is performed.

After exposure, patterning is performed to form the resist layer as theetching mask on the pillar-shape spacer forming location. Thereafter,the silicon oxide film is etched using this resist layer as the mask tocomplete the desired pillar-shape spacer 12.

Further, when the exposure of the substrate for forming the light valvefor green has been completed, the substrate is removed from the exposureequipment, another silicon substrate 2 on which a silicon oxide film andthe photoresist layer have been formed is loaded on the X-Y stage of theexposure equipment, and the exposure of the substrate for forming thelight valve for blue is performer as FIG. 11 shows.

The X-Y stage of the exposure equipment is moved to align the alignmentsubmark for blue 20 of the substrate side alignment marks 22 with thealignment submark for blue 28 of the mask side alignment marks 30, andexposure is performed.

After exposure, patterning is performed to form the resist layer as theetching mask on the pillar-shape spacer forming location. Thereafter,the silicon oxide film is etched using this resist layer as the mask tocomplete the desired pillar-shape spacer 14.

Thus, according to the method for manufacturing the pillar-shape spacersof this embodiment, the pillar-shape spacers may be formed at prescribeddeviated locations in the pixel array regions in liquid crystal lightvalves for red, green and blue by using a single spacer mask. Since themethod for forming the pillar-shape spacers of this embodiment increasesfew additional steps over conventional methods, and does not require toprovide a plurality of masks, the method is also economicallyadvantageous.

The present invention is not limited to the above embodiment, andvarious variations are possible.

For example, although the locations of pillar-shape spacers of lightvalves for each color are shifted by prescribed distances, thepillar-shape spacers may be formed at random locations, because it issufficient as long as the pillar-shape spacers of light valves for eachcolor are formed at locations that do not overlap with each other.

Although the alignment marks are cross-shaped for the ease ofdescription, any shape of marks may be used as long as alignment can beperformed practically.

In the above embodiment, although the distance between submarks of arraysubstrate side alignment marks 22 is 13 pixels long in the Y direction,and the distance between submarks of mask side alignment marks 30 is 3pixels long in the X direction and 10 pixels long in the Y direction,these are not limited to the above values.

In the above embodiment, since the distance between pillar-shape spacersfor each color is determined to be 3 pixels long both in X and Ydirections, alignment marks may be formed so that the array substrateand the mask are relatively shifted by 3 pixels long both in X and Ydirections. That is, the alignment marks shifted from each othercorresponding to the Shift amount of pillar-shape spacers for each colormay be provided.

Further in the above embodiment, although pillar-shape spacers arepatterned by shifting alignment marks on the underlying siliconsubstrate, the spacer mask may be shifted, or both alignment marks andthe spacer mask may be shifted, because underlying alignment marks andthe spacer mask side alignment marks may be relatively shifted from eachother by prescribed amounts.

Advantages of the invention

As described above, according to the present invention, a liquid crystaldisplay device with improved display properties is provided bypreventing the degradation of contrast and the occurrence of residualimages.

What is claimed is:
 1. A liquid crystal display device comprising threeseparate liquid crystal light valves for projecting on a screen imagescorresponding to red, green and blue each light valve having a pluralityof pillar-shaped spacers formed in a pixel array region for maintaininga prescribed cell gap, wherein,said pillar-shaped spacers are positionedin the pixel array region in each of said three liquid crystal lightvalves at locations where at least a part of shadows cast by thepillar-shaped spacers do not overlap with each other in projected imagesproduced by the three valves when they are superimposed on one anotheron the screen.
 2. A liquid crystal display device as set forth in claim1, wherein,said pillar-shaped spacers formed in the pixel array regionin each of said three liquid crystal light valves are located atlocations regularly shifted from each other.
 3. A liquid crystal displaydevice as set forth in claim 2, wherein,said pillar-shaped spacersformed in the pixel array region in each of said three liquid crystallight valves are provided at locations shifted from each other by anequal distance.
 4. A liquid crystal display device as set forth in claim2, wherein,said pillar-shaped spacers are located in light shieldingregions between a plurality of pixels in each of said pixel arrayregions.
 5. The display of claim 1, wherein each of the spacers is atthe intersection of a different four pixels in a matrix of pixels ineach of the light valves.
 6. The method of claim 5, wherein the spacersare arranged at fixed intervals in both an x and y direction in each ofthe matrices.
 7. The method of claim 6, wherein the position of eachspacer in each matrix is offset from the position of a correspondingspacer in the other two matrices.
 8. The method of claim 7, wherein thespacers are arranged 9 pixels from one another in each of the matricesand the position of each spacer in any one matrix is offset by at leastthree pixels from the position of any spacer in any other matrix.
 9. Ina liquid crystal display device having three separate liquid crystaldisplay valves each including a matrix of pixels producing differentcolored images that are superimposed on one another on a projectionscreen to produce a multicolored image, the method comprising:placingsupport spacers, for maintaining cell gaps in the liquid crystal displayvalves, at positions in each of the display valves that are displacedfrom positions of the spacers in the other two valves by positioningeach of the spacers at an intersection of a different four pixels in thematrix of pixels in each of the light valves so that part of shadows ofimages caused by the spacers in one valve do not overlap shadows causedby the spacers in the other two light valves when the colored imagesproduced by the three valves are superimposed on each other on thescreen.
 10. The method of claim 9, including arranging the spacers atfixed intervals in both an x and y direction in each of the matrices.11. The method of claim 10, offsetting the position of the spacers ineach matrix from the position of the posts in the other two matrices.12. The method of claim 10, wherein the spacers are arranged 9 pixelsfrom one another in each of the matrices and the position of each spacerin any one matrix is offset by at least three pixels from the positionof any spacer in any other matrix.
 13. In a liquid crystal displaydevice having three separate liquid crystal display valves eachincluding a matrix of pixels producing different colored images that aresuperimposed on one another on a projection screen to produce amulticolored image, the method comprising:placing spacers, maintainingcell gaps in the valves, at positions in each of the display valves thatare displaced from positions of the spacers in the other two valves sothat part of shadows of images caused by the spacer in one valve do notoverlap shadows caused by the spacers in the other two light valves whenthe colored images produced by the three valves are superimposed on eachother on the screen.
 14. The method of claim 13, including arranging theposts at fixed intervals in both an x and y direction in each of thematrices.
 15. The method of claim 13, offsetting the position of thespacers in each one of the matrices at fixed intervals from the positionof a corresponding spacer in the other two matrices.
 16. The method ofclaim 15, wherein the spacers are arranged 9 pixels from one another ineach of the matrices and the position of each spacer in any one matrixis offset by at least three pixels from the position of any spacer inany other matrix.